Various types of valves are used in oilfield well exploration, drilling, and production equipment. Valves are coupled to a pipeline and are typically used to shut off or turn on the flow of a fluid, such as a liquid, gas or both. Valves are typically either unidirectional or bi-directional. In a unidirectional valve, the valve has to be placed only in one unique way in a pipeline so as to match the pressure direction. In a bi-directional valve, either side of the valve can be used as the upstream side, which allows the valve to be placed in a pipeline without any specific side facing the direction of pressure. Valve sealing components are usually symmetrical for ease of installation and maintenance and to achieve bi-directionality.
A gate valve is a type of valve that includes a substantially rectangular-shaped gate that is moved by an operator in and out of the valve body to control the fluid. The operator may be manual or may be actuated hydraulically, pneumatically or electrically, for example. A gate valve also includes an annular or ring-shaped seat member that seals against the gate. Depending on gate valve design, one seat member may be disposed on either side of the gate, or alternatively, additional seat members may be disposed adjacent the seat member, which seat members are involved in the sealing of the valve. The additional seat members seal the passage between the seat member and body pocket.
A valve body pocket generally houses the seal assembly. A valve seal assembly generally includes sealing members such as the seat member adjacent the valve engaging member and other associated seat members which may be referred to as a body bushing or pocket insert, as examples. A seal assembly also generally includes at least one seal ring, which provides a seal between the various seat members, valve body pocket and the gate. Expanding gate valves utilize expanding gate assembly structures comprising a gate element and segment, which are adapted to expand transversely of one another against the sealing rings.
Another type of valve design is a plug valve, where a cylindrical plug having a bore in the center thereof is used to either block fluid flow, or to allow fluid to pass through the valve by rotating the plug. When the plug bore is aligned in parallel with the valve bore, the valve is open and fluid flows through the plug. When the plug bore is aligned perpendicular to the valve bore, the valve is closed and fluid is blocked from flowing through the plug.
Gate valves are classified as either downstream or upstream sealing. For downstream sealing gate valve designs, the sealing is done at the downstream side of the valve. The downstream side of the valve is the side farthest from the pressure source. Therefore, a valve having a downstream sealing design seals on the side of the valve farthest from the pressure source. In contrast, a valve having an upstream sealing design seals on the side of the valve closest to the pressure source.
Various types of seal assemblies have been devised for such valves. With many of these, such as where the seats are press-fit into seat pockets in the valve body, the seats must be installed or removed for repair purposes using special tools and associated costly procedures.
Several designs for valve seal assemblies and methods are described in commonly assigned patent application Ser. No. 09/911,148, filed on Jul. 23, 2001, entitled “Valve Seal Assemblies and Methods,” now U.S. Pat. No. 6,664,572, which application is hereby incorporated herein by reference.